The invention relates to a lancing system for the extraction of a body fluid from the skin of a human or animal. The lancing system comprises a needle element for lancing the skin and a lancing device, which includes a lancet drive. By the lancet drive a lancing movement is driven in a lancing direction of a needle element, the needle element being coupled with the lancet drive by means of a coupling mechanism.
Generally the body fluid extracted by means of the lancing system is blood. In some applications however, samples of interstitial fluid are also extracted. If blood as an example of a body fluid is mentioned hereafter, this is not a restriction of the generality. Blood stands only as an example for any other body fluid extractable from the skin.
For diagnostic purposes small quantities of blood are extracted from a body part, for example from the finger or the ear lobe. Lancets, which lance a wound in the body part with their tip, are used for this purpose. The prick of the lancet in the skin is performed either by specially trained personnel, who manually carries out the pricking, or by blood extraction systems, which include so-called lancing devices and lancets adapted therefor.
In the case of simple lancing devices the lancet pricks the skin with a quick movement and on reaching the reversal point is again withdrawn from the skin. After this the lancing device is removed. The user then massages the skin in the region of the prick and compresses it to promote the discharge of blood from the skin. This compression of the skin designated as “milking” is continued until an adequately large drop of blood issues from the skin. In a further step the drop of blood is applied to a test strip in order to determine the concentration of an analyte, in particular the glucose value, present in the blood. However, this procedure is tedious and also unpleasant for the user since he has to squeeze the skin in the vicinity of the wound.
In particular for diabetics who have to lance their skin repeatedly every day to determine the glucose content in the blood, lancing as free of pain as possible is important. Also important is a simplified handling of the blood extraction. Especially the “milking” which is perceived as unpleasant should be avoided. For this reason a plurality of lancing devices were developed in the prior art which comprise a large outlet opening for the lancet with a diameter of several millimeters. The front end of the housing enclosing the outlet opening in the shape of a ring forms a housing skin contact surface which is pressed against the skin. As a result of the pressure the skin bulges into the opening of the lancing device. At the same time, the internal pressure in the finger (or other body part) is increased by the contact pressure exerted, so that upon lancing of the skin by the lancet the body fluid or the blood issues spontaneously without manual massaging or “milking” being required. Products of this type are hereinafter referred to as “lancing system with expression aid”.
It has been known for some time that the pain perception is substantially influenced by the reproducibility of the lancing depth. In other words, the depth of the prick is to remain preferably the same with a plurality of lancing operations (but unchanged setting of the lancing device) separated in time in order to generate an adequate quantity of blood with a minimum prick depth (U.S. Pat. No. 5,318,584). The prick depth is determined on the one hand by the position of the reversal point of the lancing movement and on the other hand by the position of the skin upon reaching of the reversal point. The reproducibility of the position of the reversal point depends on the construction of the lancet drive. Numerous drive constructions are known which guarantee a very good reproducibility of the position of the reversal point. These include in particular rotor drives as are described in U.S. Pat. No. 5,318,584 and numerous further documents of the prior art. The present invention can be combined with various drive constructions, provided these guarantee adequate reproducibility of the position of the reversal point with a plurality of lancing operations and unchanged setting of the device. With a given quality of the lancet drive the reproducibility of the prick depth decisively depends on a reproducibly defined position of the skin during the prick.
In this regard there are particular problems with lancing system with expression aid since the bulging-in of the skin is dependent on the condition of the skin and therefore varies from user to user. Even for a particular user, the skin changes its characteristics, for example as a function of whether it is dry or moist and cold or warm respectively. For this reason the housing skin contact surface on the inner edge of the housing opening constitutes only an inaccurate reference for the lancing depth.
To solve this problem a reference element is proposed in EP 1669028 A1 which, by means of a reference element coupling mechanism, is coupled with the drive of the lancing device and thus moveable. It is moved forward within the lancing device until a contact surface formed at its front end is in contact with the skin. Thereby the variation of the bulging-in of the skin into the housing opening is detected and the restriction of the reproducibility resulting from this variation, is eliminated. According to EP 1669028 the contact pressure between the reference element and the skin surface should be low since elevated pressure counteracts the issue of blood from the lancing wound. In addition it is emphasized that after the lancing the reference element should be moved away from the lancing wound very rapidly (within a maximum of 50 msec) in particular in order to avoid contamination of the reference element by issuing blood.
According to a series of further known proposals, function improvements, including the reproducibility of the lancing depth, are to be achieved by using a lancing depth control element rapidly moved towards the skin jointly with a needle, wherein positive effects are to be achieved by the impulse on impacting the skin.
For example EP 1527736 A1 discloses a lancing device wherein a lancing unit consisting of a lancet and a lancing depth control element is moved towards the skin. During the forward phase of the lancet movement, the lancing depth control element is moved therewith until it strikes the skin. Thereafter, the tip of the lancet penetrates into the skin.
A basically similar lancing device is disclosed in U.S. Pat. No. 6,306,152 B1. It comprises a relatively large housing opening through which the skin can bulge into the lancing device. In order to stretch the skin during the lancing it is proposed to employ a spring-loaded control element which jointly with the lancet is moved in the direction of the skin during the forward phase of the lancing movement. When the control element strikes the skin the lancet moveably mounted in the control element continues to be moved in the lancing direction by its inertia until it strikes a stop of the control element. Thereby it pricks the skin. The spring used to advance the control element then retracts the control element with the lancet, thereby extracting the lancet from the skin. U.S. Pat. No. 6,929,650 B2 also describes a system wherein the lancet on the way into the skin takes along a stop structure which contacts the skin and defines the lancing depth.